Ballast tube



Sept. 5, 1961 B. F. STEIGER ET AL 2,999,216

BALLAST TUBE Filed Feb. 25, 1960 ATTO RN EYS United States Patent O 2,999,216 BALLAST TUBE Benjamin F. Steiger and 'Max Yarmovsky, Livingston, NJ., assignors to Tung-SolElectric Inc., a corporation of Delaware Filed Feb. 23, 1960, Ser. No. 1'10,172 5 Claims. (Cl. 338-20) This invention relates to a ballast tube having an improved filament which provides better operating conditions and longer life.

This application is a continuation-impart of an application tiled October 18, 1956, Serial No. 616,850, now Patent 2,928,061, issued March 8, 1960.

Ballast tubes containing an iron wire filament in an atmosphere of hydrogen at reduced pressure have been used for many years to provide a stabilized constant current for other circuit components. lt is well-known that iron wire has a temperature coefficient of resistivity such that, over an appreciable range of applied voltage, the current through the wire is substantially independent of the voltage drop across it.

Ballast tubes made of pure iron wire have several inherent defects which tend to shorten their life. During use the iron changes its crystalline orientation and as a result, the lilament becomes distorted and the characteristics of the element are changed. Also, present ballast tubes develope ihot spots on the filament which are sometime caused by crystal distortion and sometime caused by small areas having a bright clean surface in comparison to other sections of the filament which are partially oxidized. The reduced heat radiation from clean bright Iareas raises the temperature and causes changes in crystal structure.

The present invention comprises a ballast tube having a life which is at least three times the life of prior ballast tubes. No hot spots are developed on the iilarnent and and the distortion of the wire is greatly reduced, thereby retaining the resistance and constant current characteristics within a small range of values.

One of the objects of this invention is to provide an irnproved ballast tube which avoids one or more of the disadvantages and limitations of prior art tubes.

Another object of the invention is to increase the life of ballast tubes.

Another object of the invention is to retain the operating characteristics of a ballast tube during its life.

Another object of the invention is to eliminate hot spots on the filament.

Another object of the invention is to reduce the lament distortion during the useful life of the tube.

'Ihe invention comprises a ballast tube having an envelope in which an iron wire is mounted on insulating supports. Lead-in conductors `are connected to the iron wire for connection to an external circuit. The iron wire is first plated with a thin lm of nickel or gold and then plated with a lm of platinum. The envelope is filled with an atmosphere of inert gas at a reduced pressure.

For a better understanding of the present invention, together with other and further objects thereof, reference is made to the following description taken in connection with the accompanying drawings.

ICC

FIG. l is a side view of the ballast tube with parts broken away to show the internal construction.

FIG. 2 is a cross sectional view of the tube shown in FIG. l and is taken along line 2-2 of that figure.

FIG. 3 is a detailed view, greatly enlarged, of a portion of the ballast tube showing the insulator plate, the plated iron wire, and one of the supporting wires.

FIG. 4 is a' cross sectional view, greatly enlarged, showing the plated iron Wire.

iFlG. 5 is a cross sectional View similar to FIG. 4 taken along line 5 5 of that figure.

Referring now to FIGS. l, 2, and 3, the ballast tube includes an envelope 10 supported on a base ll which contains a plurality of contact pins 12 for connection with an external circuit. On the inside of the envolepe an iron wire 13 is mounted on insulating disks 14 and 15. These disks are generally held in position by one or more heavy supporting wires 16 although any other type of supporting means may be employed. ln the example shown, a grommet 17 (FIG. 3) is employed to grip the insulating disks 14 and 15, these grommets having small ns 18 which may be soldered or welded to the supporting wires 16.

The iron wire as indicated in FIGS. 4 and 5 is plated with a thin iilm of nickel or gold, and then plated with a covering of platinum 2li. The thickness of the plating7 is such that the weight of the wire is increased about six percent.

When this wire is mounted in its envelope, the envelope is filled with an inert gas at about twice the pressure of prior art tubes; that is, about 12 millimeters of mercury. The increased pressure causes an increased heat conduction from the filament to the envelope walls but this `additional dissipation of heat is counteracted by the reduced radiation characteristics of the platinum surface. Inert gases such as hydrogen, helium, argon, zenon, or kiypton have been tried and found to Work well with this type of construction.

Ballast tubes manufactured in accordance with the above described characteristics have exceptional long life (in many cases over 4,000 hours) and are not subjected to changing characteristics ldue to hot spots or other lilament changes.

The foregoing disclosure and drawings are merely illustrative of the principles of this invention and are not to be interpreted in a limiting sense. The only limitations are to be determined from the scope of the appended claims.

We claim:

l. A ballast tube which passes constant current for a range of applied voltages comprising, an envelope containing an iron Wire with `a first covering of nickel and a second covering of platinum, said envelope containing an inert gas at reduced pressure.

2. A ballast tube which passes constant current for a range of applied voltages comprising, an envelope containing -an iron wire with a iirst covering of nickel and a second covering of platinum, and lead-in conductors connected to the iron wire for external connection, said envelope containing an inert gas at reduced pressure.

3. A ballast tube as set vforth in claim 2 wherein the pressure of the inert gas is greater than l0 millimeters of mercury.

:2,999,216 v l. Y ,t t Y 3 Y Y 4 4. A ballast tube as set forth in claim 2 wherein the Weight of the Wire is increased about six percent, and thickness of the nickel and platinum films is such that lead-in conductors connected to the iron wire for conthe Weight of the Wire is increased about six percent. nection to an external circuit.

5. A ballast tube which passes `constant current for a restricted range of applied voltages comprising, an en- 5 References Cited in the fue 0f this Patent velope, an iron wire mounted within the envelope in an UNITED STATES PATENTS atmosphere of an inert gas at a pressure of more than l0 millimeters of mercury, said iron Wire covered with a 'e'l '1F/f3' g first iilm of nickel and a second ilm of platinum, the 2685535 Nack g Au 3 1954 film, of platinum being at least twice as thick as the lm l@ g' of nickel, the thickness of both lms being such that the 2928061 Steiger et al' Mar' 8 1960 

1. A BALLAST TUBE WHICH PASSES CONSTANT CURRENT FOR A RANGE OF APPLIED VOLTAGES COMPRISING, AN ENVELOPE CONTAINING AN IRON WIRE WITH A FIRST COVERING OF NICKEL AND A SECOND COVERING OF PLATINUM, SAID ENVELOPE CONTAINING AN INERT GAS AT REDUCED PRESSURE. 